The automatic sensing device of traditional industries is mainly applied to sense the parameters, such as position, speed, rotational speed (RPM) and count of the objects. We usually classify types of sensors as contact or contactless. The contact type has to directly contact with the tested object to get moving information, such as micro switch or limit switch, but it is not suitable for applying to precision component process because the contact area is easy to wear the surface of the tested object to affect the next precision process. The traditional contactless sensing device mainly uses magnetic induction technique or optical technique. The magnetic induction technique is mainly by using Hall Effect, which the change of magnetic flux from detecting the output current of a circuit results in an output voltage (Hall voltage), such as reed switch, proximity switch, or tachometer. But it has the disadvantages of being effected by electronic noise easily, being influenced by temperature variation, and consuming more power. The sensing device using optical technique is judging if the light beam emitted by a light source is received or not to output signals, and the basic elements of the device have to comprise an encoder, a light emitter and a light receiver. If the elements further comprise a processor, the cost will be high. In addition, the light beam has to emit straightly, so that it is not suitable for applying to narrow-space factory.
Furthermore, the installation of the traditional sensing device must depend on the shapes or applications of the tested object(s). It is limited to have to be arranged on the tested object(s) in advance, such as tachometer. The Hall sensor and the encoder have to be mounted on a shaft in advance to further sense the rotational speed of the shaft. If operators also want to measure the moving speed of the glass substrate, the rotational speed sensor, such as tachometer with the encoder, is not applicable to be used and another position sensor, such as micro switch or limit switch, must be further prepared and mounted. Therefore, the traditional sensing device has the disadvantages of the rigid installation, so that the applications are limited, and the additional or different spare parts with higher cost are prepared in advance. A novel contactless sensing device with flexible installation and portable function is necessary.